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Recently, for reduction of PM emission from diesel engine, low sulfur diesel fuel was introduced and commercialized. There are some reports for effect of fuel sulfur on PM characteristics by using engine dynamometer tests. However, it is difficult to understand mechanism of PM formation and effect of fuel sulfur on PM formation process. Thus, investigation by a simple flame is effective way for understanding detail PM formation process. In this paper, effect of sulfur content in fuel on PM characteristics was investigated by using laboratory-scale PM generator. Test fuels were diesel and surrogate diesel fuel, and sulfur concentration in the surrogate fuel was controlled with thiophene addition. Effects of fuel sulfur on PM were clarified with characteristics of PM obtained from PM number distribution measurements and PM compositions analysis.

In this study, using a droplet dripping and evaporation test rig, over ten thousands droplets of diesel and bio-diesel fuels were dripped on a hot surface repeatedly, and evaporation deposits formed from them were quantitatively analyzed. Results show that wet-dry condition and hot surface temperature were main controlling factors of deposits development. Empirical equations of deposits development were derived from the experimental results. Further carbonaceous evaporation deposits from RME were around ten times serious than diesel fuel. The main reason of it was that bio-diesel fuel was produced from various plant oils through esterification and it was liquid phase chemical reaction process with no hot distillation, so that thermal stability of bio-diesel fuel was poor.